Trivalent lanthanide ions represent a metal-centered probe of protein structure and function in solution which is being developed and exploited. This type of probe, applicable principally to calcium-binding proteins and to nucleic acids, involves the measurement of environmentally-sensitive lanthanide ion luminescence lifetimes. Measurements on dilute protein solutions for a number of different trivalent lanthanide ions, bound at calcium ion sites, are made possible by the use of a high-power, flash-lamp pumped, dye laser as an excitation source. The luminescence lifetime measurements are used to determine the number of water molecules coordinated to the metal ion. Inter-metal ion nonradiative energy-transfer (lanthanide to transition metal ion and inter-lanthanide) measurements will be exploited as a metal-metal distance probe to gain knowledge about protein structure in solution. The luminescence emission bands are examined under high resolution to yield information concerning the details of the metal ion coordination. Using a pulsed nitrogen laser pumped dye laser, time-resolved emission and excitation spectra are being used to study complex equilibria in solutions of various proteins and model systems. The fluorescent aromatic aminoacid to lanthanide ion energy transfer step which accounts for the large luminescence intensity enhancements observed in some systems will be investigated. The techniques developed will be applied to the proteins: thermolysin, paravalbumin, taka amylase, troponin C, bovine pancreatic deoxyribonuclease A, phosphoglycerate kinase, and phospholipase A2, as well as to tRNA.